One important area of development in the area of absorbent articles of the above-mentioned type is the control of odourous compounds forming typically after the release of body fluids, especially over a longer period of time. These compounds include fatty acids, ammonia, amines, sulphur-containing compounds and ketones and aldehydes. They are present as natural ingredients of body fluids or result from degradation processes of natural ingredients such as urea, which is broken down by microorganisms or bacteria occurring in the urogenital flora to ammonia.
Various approaches exist to suppress the formation of unpleasant odours in absorbent articles. WO 97/46188, WO 97/46190, WO 97/46192, WO 97/46193, WO 97/46195 and WO 97/46196 teach for instance the incorporation of odour inhibiting additives or deodorants such as zeolites and silica. The absorption of bodily liquids reduces however the odour inhibiting capacity of zeolites as soon as these become saturated with water, as mentioned for instance in WO 98/17239.
A second approach involves the addition of lactobacilli with the intention of inhibiting malodour-forming bacteria in the product. The incorporation of lactobacilli and their favourable effect are disclosed for instance in SE 9703669-3, SE 9502588-8, WO 92/13577, SE 9801951-6 and SE 9804390-4.
Moreover, it is known from WO 98/57677, WO 00/35503 and WO 00/35505 that partially neutralized superabsorbent materials (acidic superabsorbent materials) counteract the formation of unpleasant odours in absorbent articles. However, acidic superabsorbent materials absorb lower amounts of body fluid compared to regular superabsorbent materials (in the following also referred to as superabsorbent polymer, SAP). The absorbent articles described in the above-mentioned WO 98/57677 may additionally contain fluffed cellulose pulp having a pH value below 7, preferably below 6.
Further, U.S. Pat. No. 6,852,904 describes cellulose fibers treated with acidic odor control agents and their use in absorbent products.
Various known odour control systems are however not effective enough or loose their effectiveness too quickly to be accepted by consumers of absorbent products.
Therefore, an ongoing demand exists in the art for effective odour-control systems in absorbent articles.
From other technical areas it is further known that organic zinc salts of unsaturated hydroxylated fatty acids such as zinc ricinoleate are deodorizing active ingredients (see for instance DE 1792074 A1, DE 2548344 A1 and DE 3808114 A1).
It is one technical object of the present invention to overcome deficiencies discussed above in connection with the prior art.
It is one further technical object to provide an absorbent article having an efficient odour control system.
It is one further technical object of the present invention to considerably reduce or eliminate ammonia formation in absorbent articles.
Further objects will become apparent from the following description of the invention.